Polyvinylidene fluoride is excellent in such properties as heat resistance and chemical resistance. It also has a large differential between the melting point and the pyrolysis temperature, and thus is easy to process. Polyvinylidene fluoride is thus used in various applications.
Known methods of producing polyvinylidene fluoride or other fluoropolymers include emulsion polymerization, suspension polymerization, solution polymerization, and bulk polymerization. The emulsion polymerization is a method that includes polymerizing fluoromonomers in the presence of a surfactant to provide an aqueous dispersion of a fluoropolymer.
The surfactants conventionally used are perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), which could adversely affect the environment.
In such situation in the art, Patent Literature 1 discloses production of a fluoropolymer aqueous dispersion using a bifunctional fluorinated surfactant represented by the formula:A-Rf-B  (I)wherein A and B are the same as or different from each other, and are each —(O)pCFX—COOM (where M=NH4, an alkali metal, or H; X=F or CF3; p is 0 or an integer equal to 1); Rf is a linear or branched perfluoroalkyl or (per)fluoropolyether chain that allows the surfactant of Formula (I) to have a number average molecular weight of 300 or 1,800, preferably 500 or 1,600, and more preferably 600 or 1,200.
Patent Literature 2 discloses production of a dispersion of a fluorinated polymer using one or more anionic surfactants having Formula (1):Y′-(P1)n—CH(Y)-(P2)n′-Y″  (1)wherein Y, Y′, and Y″ are each an anionic or nonionic group, but at least one of Y, Y′ and Y″ is an anionic group and at least one of the others of Y, Y′ and Y″ is a nonionic group; P1 and P2 are the same as or different from each other, and are each a C1 to C10, preferably C1 to C6 linear-chain or branched alkylene group that may optionally have one or more unsaturations; and n and n′ are the same as or different from each other and are each 0 or 1.
Patent Literature 3 discloses production of a low molecular weight polytetrafluoroethylene by emulsion polymerization in the presence of a fluorine-containing compound represented by the following Formula (1):X—(CF2)m—Y  (1)wherein X represents H or F, m represents an integer of 3 to 5, Y represents —SO3M, —SO4M, —SO3R, —SO4R, —COOM, —PO3M2, or —PO4M2 (M represents H, NH4, or an alkali metal, R represents a C1 to C12 alkyl group) and a reactive compound that has a functional group reactable in radical polymerization and a hydrophilic group.